One hardly expects, in the course of normal politics, to see Sen. Bernie Sanders, I-Vermont, thanking the billionaire brothers Charles and David Koch. And yet here we are. “Thank you, Koch brothers,” his Monday night tweet began, “for accidentally making the case for Medicare for All!” You see, the market-oriented Mercatus Center, which takes funding from the Kochs, has a new report out on the costs of the senator’s pet project.